Iím going to build SLís Phoenix, but am attracted to the all in one design of the Orion. For one thing it'll be easier in a shared room.to move around two boxes rather than four. So Iím thinking of mounting the Phoenix midrange baffle onto the Orion H frame woofer cabinets.

The W frame is wider and lower; the H frame resonance is higher (but with an XO at 120 Hz, both resonances are relatively outside the effective range of the woofers) and by the way the drivers are mounted - the W frame has the benefit of force cancellations.

Beginning to think that the best all round compromise is to do a woofer Ďboxí Orion - H style, sitting underneath the midrange baffle, but just sitting off it, isolating vibrations.
This would still have the integrated look, and allow experimenting with different-better woofer locations, when "she who likes to be obeyed" is away and/ or I move to a bigger room.

It does mean I'd need a pair of inverted U shaped brackets to support the midrange baffle, straddling the woofer box. Though these could be used as a base, to support midrange driver brackets a la Orion Revision 0.1. This may be a simpler path to further midrange driver isolation than the Phoenix midrange driver spline arrangement, which I hear can be fiddly to construct.
I suspect that Phoenix XO would not require any change, but I still need to confirm or check this??
Thanks

Any kind of a hybrid.....W or H, with Orion or Phoenix style main panels is do-able. There might be some changes required to the crossover system depending upon how you implement it. Generally, a W-baffle would probably require a notch filter and an H-baffle probably wouldn't. The fore/aft position of the mid-panel relative to the bass baffle might also require some time delay.

The force cancellation of the W-frame woofer is desirable if your floor construction/support is marginal. If you're on a slab or some other solid base then I don't believe the H-frame construction would be a problem.

I think isolating the mid-panel from the bass is desirable in all instances.